You cannot remove subsidiary: xxx because this record is used on a transaction for subsidiary: xxx
This error happens when you update or add another subsidiary to an item record.
Enter the information in your CSV like this:
Name | Subsidiary
Apple | Parent Company | Parent Company: US: California | Parent Company: US: California: Sub A
Because the Subsidiary field in the item record is a multi-select field type, values in the CSV file are entered in one row with a delimiter, for example, the pipe, (|).
On the File Mapping page, map Name to Item Name/Number and Subsidiary to Subsidiary.